You’re running into an infinite loop caused by cycles within your data, e.g.: 1 > 2 > 3 > 2 > … . The solution is to keep track of the rows that have already been “consumed”. Due to limitations in CTEs, this has to be done by including the history within each CTE row, e.g. by assembling the path followed to arrive at each row. You can uncomment the , Path
on the final select
to see what is going on.
-- Sample data.
declare @ACC as Table ( AccNo Int, Property Char );
insert into @ACC values
( 1, 'A' ), ( 1, 'B' ), ( 2, 'A' ), ( 2, 'C' ), ( 3, 'C' ), ( 4, 'D' );
select * from @ACC;
-- Recursive CTE.
with Groups as (
select distinct AccNo, AccNo as LinkedAccNo,
Cast( '|' + Cast( AccNo as VarChar(10) ) + '|' as VarChar(1024) ) as Path
from @ACC
union all
select G.AccNo, A.AccNo, Cast( Path + Cast( A.AccNo as VarChar(10) ) + '|' as VarChar(1024) )
from Groups as G inner join -- Take the latest round of new rows ...
@ACC as AP on AP.AccNo = G.LinkedAccNo inner join -- ... and get the Property for each ...
@ACC as A on A.Property = AP.Property -- ... to find new linked rows.
where G.Path not like '%|' + Cast( A.AccNo as VarChar(10) ) + '|%' )
select AccNo, LinkedAccNo -- , Path
from Groups
order by AccNo, LinkedAccNo;